The present invention relates to a method of defrosting and, more particularly, to a method of defrosting an evaporator coil of a transport temperature control unit.
Straight trucks and tractor-trailers are often used as a means to transport cargo that must be maintained at a predetermined or desirable temperature during transportation in order to preserve the quality of the cargo. This cargo may be food, agricultural goods or various other temperature critical items. Hereinafter, any vehicle that transports cargo that must be maintained at a predetermined temperature during transportation will be referred to as a transportable vehicle or a transport vehicle. Hereinafter, the term cargo means any item that is transported, stored or otherwise supported within a conditioned space of a transport vehicle that must be maintained at a predetermined temperature.
Transport vehicles that transport such temperature sensitive cargo include a conditioned space. The temperature within the conditioned space is controlled within a temperature range adjacent to a selected thermal setpoint by a temperature control unit. Some transport vehicles have a plurality of conditioned spaces, which may be maintained at the same thermal setpoint or varying thermal setpoints by the unit.
The temperature control unit can be programmed to cool or heat the conditioned space to the thermal setpoint. Frost can build-up on the temperature control unit when the temperature control unit is cooling the conditioned space. More particularly, frost or condensate can build-up on an evaporator coil of the temperature control unit and decrease the efficiency of the temperature control unit while in the cooling mode. Defrost cycles are typically utilized to remove the condensate. A defrost cycle is performed by circulating a heated fluid through the evaporator coil. The heat from the fluid is passed to the evaporator coil, causing the condensate to melt. The temperature control unit returns to the cooling mode after defrosting and cools at a greater efficiency due to the decreased build-up of condensate on the evaporator coil.
Many varying types of defrost cycles exist and include manual defrost cycles, fixed time defrost cycles and static pressure defrost cycles. A person initiates and terminates a manual defrost cycle, while the fixed time defrost cycle initiates and terminates on a fixed timer that is programmable with a time period. The static pressure defrost cycle initiates when the static pressure across the evaporator coil reaches undesirable levels and terminates when the static pressure is at a desirable level.
One problem with the defrost cycle of the above-described temperature control unit is that the defrost cycle of the unit is initiated and terminated by a person.
Another problem with the defrost cycle of the above-described temperature control unit is that the defrost cycle of the unit operates on a fixed timer for varying environments and conditions within the conditioned space.
A further problem with the defrost cycle of the above-described temperature control unit is that the defrost cycle of the unit may operate based on an inaccurate static pressure reading.
The present invention provides a method of defrosting an evaporator coil of a transport temperature control unit that substantially alleviates one or more of the above-described and other problems.
More particularly, the invention provides a method of defrosting an evaporator coil of a transport temperature control unit. The transport temperature control unit may be operable to circulate refrigerant through the evaporator coil for cooling a conditioned space within a transportable vehicle and may be operable to maintain an air temperature of the conditioned space within a range of a desired temperature. The method includes providing a control sensor, sensing the air temperature of the conditioned space with the control sensor, comparing the air temperature and the desired temperature of the conditioned space, enabling a defrost cycle that is operable to remove condensate from the evaporator coil when the air temperature is greater than the desired temperature.
It is another feature of the invention to provide a method of defrosting an evaporator coil of the transport temperature control unit. The temperature control unit may be operable to circulate refrigerant through the evaporator coil for cooling a conditioned space within a transportable vehicle. The method includes initiating a first defrost cycle for removing condensate from the evaporator coil and terminating the first defrost cycle. The first defrost cycle has a defrost duration time. The method also includes establishing a defrost interval time dependent on the defrost duration time and initiating a second defrost cycle after the defrost interval time expires.
It is a further feature of the invention to provide a method of defrosting an evaporator coil of a transport temperature control unit. The transport temperature control unit may be operable to circulate refrigerant through the evaporator coil for cooling a conditioned space within a transportable vehicle and may be operable to maintain an air temperature of the conditioned space within a range of a desired temperature. The method includes sensing the air temperature of the conditioned space, enabling a warm load defrost when the air temperature of the conditioned space is greater than the desired temperature, initiating a first defrost cycle for removing condensate from the evaporator coil and terminating the first defrost cycle. The first defrost cycle has a defrost duration time. The method also includes establishing a defrost interval time dependent on the defrost duration time and initiating a second defrost cycle after the defrost interval time expires.